Imaging mass spectrometer

Abstract

An MS2 analysis for one precursor ion is performed to collect data on each micro area within a measurement target area (S1). A plurality of product ions are extracted based on those data (S2), and a mass spectrometric (MS) imaging graphic is created for each m/z of the product ion (S3). Hierarchical cluster analysis is performed on the created MS imaging graphics to group the product ions based on the similarity of the graphics (S4). Product ions having similar distributions are sorted into the same group. Such a group of ions can be considered to have originated from the same compound. Accordingly, the intensity information of a plurality of product ions is totaled in each group and for each micro area (S5), and an MS imaging graphic is created based on the totaled intensity information (S6). Even if there are a plurality of compounds overlapping the precursor ion, the influence of the overlapping can be eliminated through those steps. Thus, a graphic having a higher level of SN ratio, sensitivity and dynamic range than an MS imaging graphic obtained at a single product ion can be created and displayed.

The invention claimed is: 
     
       1. An imaging mass spectrometer for creating a graphic reflecting a distribution of a substance within a two-dimensional area on a sample, based on data collected by performing an MS n  analysis on each of a plurality of micro areas set within the two-dimensional area (where n is an integer equal to or greater than two), the imaging mass spectrometer comprising:
 a detector, 
 an ion guide configured to pass ions from the sample to the detector; and 
 at least one processor, including
 a) a distribution similarity determiner for determining a similarity in two-dimensional intensity distribution of a plurality of obtained product ions, based on data obtained by the detector in an MS n  analysis for a same precursor ion on each micro area, and for grouping together product ions having a high degree of similarity in two-dimensional intensity distribution; 
 b) an intensity information calculator for totaling or averaging, for each micro area, intensity information of a plurality of product ions sorted into one group by the distribution similarity determiner, to calculate intensity information due to the plurality of product ions in each micro area; and 
 
 a graphic creator for creating a mass spectrometric imaging graphic based on the intensity information due to the plurality of product ions in each micro area obtained by the intensity information calculator. 
 
     
     
       2. The imaging mass spectrometer according to  claim 1 , wherein:
 the distribution similarity determiner determines the similarity in two-dimensional distribution of a plurality of product ions by hierarchical cluster analysis. 
 
     
     
       3. The imaging mass spectrometer according to  claim 1 , wherein the at least one processor further comprises:
 a product ion extractor for extracting a mass-to-charge ratio of a product ion based on data obtained by an MS n  analysis for the same precursor ion in each micro area. 
 
     
     
       4. The imaging mass spectrometer according to  claim 3 , wherein:
 the product ion extractor selects a product ion with reference to a given standard mass spectrum. 
 
     
     
       5. The imaging mass spectrometer according to  claim 2  wherein the at least one processor further comprises:
 a product ion extractor for extracting a mass-to-charge ratio of a product ion based on data obtained by an MS n  analysis for the same precursor ion n each micro area.